3. Homeostasis Flashcards
Define Homeostasis
Homeostasis is the maintenence of a constant internal environment
Define Negative feedback control mechanism
This is when a deviation from a set point/norm value will result in effectors being activated to restore the set point value. (eg effectors being muscle or gland)
Give an example of a negative feedback control mechanism
Control of core body temperature via thermoregulation
Define positive feedback mechanism
An initial stimulus produces a response that exaggerates or enhances the change in the original conditions, rather than opposing it. I.e a deviation from the set point results in processes that enhance that deviation further from the norm
Give an example of a positive feedback mechanism
Childbirth
What are the two different systems employed in homeostatic regulation
Autoregulation
Extrinsic regulation
Define autoregulation
This describes local level, cellular/tissue level response to environmental change. Eg a change in the oxygen concentration will triger chemicals that widen/dilate blood vessels.
List the three components of a homeostatic regulatory mechanism
Receptor, detects environmental stimuli
Control center, recieves and processes information
Effector, a cell or organ which responds to commands from control centre
Define extrinsic regulation
This involves nervous/endocrine control. For example, during exercise, the nervous system issues commands to increase heart rate so blood circulates faster
Why is homeostatic regulation important
Because it is important to prevent harmful changes in body tissue fluid composition.
Define set point
This is a value at which a controlled variable should be maintained.
Define negative feedback control
aims to maintain a controlled variable at its set point. Controlled variable is some aspect of the internal environment, like blood pressure or plasma
Describe briefly the process of thermoregulation
The set point core body temperature is 37 degrees.
If temperature rises above core temp, receptors fire to the control centre.
Control centre fires to 2 target effectors.
1) Muscle tissue lining the walls of the blood vessels
2) sweat glands.
Blood vessels dilate to increase the skin surface blood flow.
Skin acts as a radiator by loosing heat to environment via sweat. Sweat evaporates.
As the set point for temp is restored, blood flow to skin returns to normal levels.
Explain the two ways in which heat loss is achieved in the event of elevated core body temperature ( >37.2 degs)
Increased blood flow to skin surface via skin capillaries.
Increased sweating
The control of body temperature can also be thought of as a thermostat. Describe this process
Set point = normal room temp
Stimulus = room temperature rises (deviation from sp)
Receptor = thermometer (detects change and sends info to control centre)
Control centre = Thermostat, sends commands to the effector to switch on
Effector = AC. unit, which turns on. effector then acts to lower the temp, and restore the room temp to within normal range.
Give an example of an effector
muscle or gland
Give an example of a receptor
sensory receptor cells
Describe how blood pressure is regulated via homeostasis
Baroreceptors detect fall in blood pressure
baroreceptors fire implumses to the c.c via the Glossopharyngeal nerve in the medulla oblongata
Medulla fires to the heart and blood vessels via autonomic to increase cardiac output and vasoconstriction
Effectors = heart and blood vessels which increase blood pressure and vasoconsriction
State the name of the nerve that baroreceptors fire impulses along to the medulla oblongata
Glossopharyngeal nerve
In control of blood pressure, the medulla oblongata fires impulses to the heart and blood vessels along which nerves
The autonomic nerves
Explain positive feedback mechanisms
This is where initial stimulus causes a response which continually reinforces itself.
Give some examples of positive feedback mechanisms
Action potentials in nerves
Ovulation
Blood Clotting
Explain how the process of clotting is a positive feedback mechanism
Damage to blood vessel causes:
activation of clotting factors
causes activationof thrombin
causes formation of a blood clot
Which type of response is the nervous system involved in
Rapid, short term effects that last seconds usually
Which type of responses/effects is the endocrine system involved in
Long term effects.
examples include growth and metabolism
What are thyroid hormones involved in
Metabolism control
What are the features of nerves from the autonomic nervous system
CNS has a preganglionic neuron.
Peripheral ganglion is called a postganglionic neuron.
these both fire to a target cell.
Contains Parasympathetic and sympathetic nervous system
Describe the Parasympathetic Nerve
- Preganglionic neuron coming out of the cranial and sacral vertebrae regions
- Preganglionic fibres are long. Postganglionic fibres are short.
- Preganglionic fibres releases Acetylcholine (ganglionic transmitter) at the synapse. This binds to the nicotinic receptor on the short postganglionic fibre which releases acetylcholine (neurotransmitter) that activates muscarinic receptor on the target organ
Describe the Sympathetic Nerve
- Preganglionic neuron out of the spinal cord at the thoracic and lumbar vertebrae regions.
- Preganglionic fibres are short. Postganglionic fibres are long.
- Pre-g fibre release acetylcholine (ganglionic transmitter) at the synapse.
- Nicotinic receptor is activated.
- Impulse travels along long Post-g fibre and releases norepinephrine/noradrenaline (neurotransmitter).
- Alpha & Beta adrenergic receptors on target organ are activated.
How is adrenaline/ epinephrine produced?
Adrenal medulla receives impulse from pre-g sympathetic fibre into the internal adrenal medulla.
Acetylcholine is released, which stimulates nicotinic receptors on chromaffin cells,
Chromaffin cells produce and release epinephrine or adrenaline into the circulation.
Adrenaline has similar effects to noradrenaline
Define Efferent Pathways
Efferent pathwayscarry signals away from the central nervous system. Essentially, they are signals that your brain sends to tell your body to do something, like blinking.
Define Afferent Pathways
Afferent signals come from outside stimuli and tell your brain what they are sensing, such as temperature.
